Hi Thus my earlier set of posts about this point, and which CPLD's were the better ones to use for this sort of thing.
Bob On Mar 18, 2010, at 6:14 PM, Bruce Griffiths wrote: > You need to select the CPLD with some care. > Typically a low power CMOS CPLD uses an internal state machine to transfer > the configuration data sored in internal EEPROM (or similar) to internal CMOS > RAM cells that control the CPLD internal interconnections/routing. > > This intialisation process occurs during power up. > After this initialisation the EEPROM storage is powered off to reduce the > static power consumption. > Some CPLDs turn the internal initialisation state machine oscillator off when > this process is complete, some do not. > > Thus the internal intialisation state machine oscillator is a potential > source of unwanted asynchronous phase modulation of the divider outputs. > > Bruce > > Bob Camp wrote: >> Hi >> >> I think I'd just take the design over to a reasonable CPLD and be done it, >> if you are trying to improve it's floor. Having everything on a single >> "lump" of high speed silicon takes care of a lot of issues. >> >> Bob >> >> -----Original Message----- >> From: [email protected] [mailto:[email protected]] On >> Behalf Of David C. Partridge >> Sent: Thursday, March 18, 2010 8:41 AM >> To: 'Discussion of precise time and frequency measurement' >> Subject: Re: [time-nuts] Frequency divider PCB: Current status >> on"pre-orders", and pointers to documentation. >> >> I've just had in interesting offline chat with Warren S. >> >> Basic outline is that this divider is plenty good enough to use with e.g. a >> TBolt (which was my design target), and probably also for the less than >> totally committed time nuts. >> >> To quote him: >> >> "What I'm saying is does not meet the Nut cases description of a low noise >> buffer / divider." >> For good performance, do make absolutely certain that the power supply for >> this board isn't fed from the same PSU as your Rb or GPSDO, or if it is, >> make sure you take the regulated 12V from that supply and feed this board >> through another stage of cleanup using a 5V linear regulator and decoupling >> caps right close to the power input connector. Linear supply rather than >> switched (I admit that mine is switched, then post regulated). Star >> grounding of course. >> >> But for the ultimate time nuttery level of low jitter (low pS level), the >> following changes would NEED to be made. >> >> 1) Transformer coupled input clock shaper with multi-stage filtering to >> restrict input fed to comparator to only the intended single input frequency >> (10MHz). >> >> 2) Change the power supply to the board to be (say) 12V or 9V. Then use >> several 5V on board regulators to feed: >> >> a) the clock shaper >> b) the main '163 divider >> c) the 4017 divider chain >> d) each 74AC541 output driver and related FFs. >> >> Did I get that right Warren? >> >> This ensures that if e.g. the switched output is set for 1Hz, that the 5V >> supply for the other parts of the board doesn't twitch in sympathy when the >> '541 switches. >> >> 3) Maybe use BIG earth bond terminal and feed +ve supply in on single >> header. >> >> Warren, please jump in to add further points >> >> Warren is of the view that using COGs and thin film resistors isn't >> necessary except possibly to use thin film parts for R4& R5 >> >> Regards, >> David Partridge >> Email:[email protected] >> >> -----Original Message----- >> From: [email protected] [mailto:[email protected]] On >> Behalf Of David C. Partridge >> Sent: 17 March 2010 18:28 >> To: [email protected]; [email protected]; >> [email protected]; [email protected]; >> 'Discussion of precise time and frequency measurement' >> Subject: [time-nuts] Frequency divider PCB: Current status on >> "pre-orders",and pointers to documentation. >> >> The current situation is that I have almost enough statements of intent to >> get to the magic 50 which will allow a price of GBP14.50 per board plus >> delivery. For the avoidance of doubt, this is the price for a bare PCB, >> not for a kit, and definitely not for a made up board. >> >> I intend to "keep the book open" until 18:00 Zulu (UTC or GMT) on Sunday >> 21st March, I will then count up what I have and order that many boards (and >> maybe a few over to get a nice round number). >> >> I've received numerous reqeusts for the design documentation, schematic, and >> a bill of materials >> >> They can all be downloaded from my website, but there's no way (yet) to >> navigate to them (a round tuit problem). >> >> Write up: >> >> <http://www.perdrix.co.uk/FrequencyDivider/Frequency%20Divider%202.pdf> >> >> Schematic: >> >> <http://www.perdrix.co.uk/FrequencyDivider/Frequency%20Divider%202%20Schemat >> ic.pdf> >> >> and BOM: >> >> <http://www.perdrix.co.uk/FrequencyDivider/Frequency%20Divider%202%20Bill%20 >> of%20Materials.pdf> >> >> The schematic and write up have both been updated today, and the BOM is new >> today. >> >> For those who worry about SMT soldering, you don't need a reflow oven, it >> can all be done with tweezers, a small tipped iron, fine solder wire, and >> liquid flux (or a flux pen). A good pair of strong reading glasses helps >> too! See: >> >> <http://www.curiousinventor.com/guides/Surface_Mount_Soldering/101> >> >> I've also had questions on part pricing: Back in 2008, the cost to populate >> one PCB using a MAX999, thick film resistors, and standard (X7R) chip >> capacitors was about GBP28 including Molex headers and SMB sockets. I >> don't expect it to be massively different now. I'm afraid I don't have >> full parts kits, and the necessary up front costs to do so is more than my >> finances allow at present. >> >> FWIW, the ADCMP600 is a bit pricier than the MAX999, and is supposed to be >> "better", though I'm not sure in what respects it is better. >> >> If you want the lowest possible level of phase noise, you would follow the >> bill of materials recommendations and use thin film resistors and C0G >> capacitors in the clock shaper part of the circuit at the very least, but >> this adds considerably to the cost (for example 100nF C0G 1206 capacitors >> are about 1 pound each, while an X7R part is only a few pence). >> >> Regards, >> David Partridge >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
